How much concrete for a 10 ft round slab?
A 10 ft diameter slab at 4 in thick needs 26.2 cubic feet, or 0.97 cubic yards, before waste. Add 10% for about 1.07 cubic yards.
Circle calculator
Concrete Circle Calculator
Find the concrete volume for a round slab, circular patio, fire-pit pad or Sonotube. Enter the diameter and pour thickness; the calculator returns cubic yards, cubic metres, bags and cost.
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How to calculate concrete for a circle
Circle volume = π × radius² × thickness. Radius is half the diameter. Convert thickness to feet before multiplying, then divide cubic feet by 27 for cubic yards.
Example: 10 ft diameter circle at 4 in thick
The radius is 5 ft. π × 5² × (4 ÷ 12) = 26.2 cubic feet. Divide by 27 to get 0.97 cubic yards. Add 10% waste for about 1.07 cubic yards, or roughly 50 × 80 lb bags.
Common circular slab sizes at 4 in thick
| Size | Concrete | 80 lb bags* |
|---|---|---|
| 8 ft diameter | 0.62 cu yd | 29 |
| 10 ft diameter | 0.97 cu yd | 46 |
| 12 ft diameter | 1.40 cu yd | 66 |
| 15 ft diameter | 2.18 cu yd | 102 |
*Before waste. Add 5–10% for spillage and uneven subgrade.
Tips for ordering concrete for a circle
- Measure the diameter across the widest point, not the radius.
- Add 5–10% waste because circular forms and uneven subgrade can leave gaps.
- For a Sonotube, use the tube diameter and the pour height as the thickness.
- Use a two-way rebar grid or a ring of reinforcement for structural round pads; follow the plan.
Concrete Circle Calculator FAQ
How do I calculate concrete for a Sonotube?
Use the circular calculator with the tube diameter and the pour height as the thickness. A 12 in tube filled 4 ft high is about 0.12 cubic yards, or 6 × 80 lb bags before waste.
How many bags of concrete for a 12-inch Sonotube?
A 12 in diameter tube filled 4 ft high needs about 3.14 cubic feet, or 0.12 cubic yards. That is about 6 × 80 lb bags before waste. Check the tube height and bag yield before ordering.
How much concrete for a circular patio?
A 12 ft diameter patio at 4 in thick is about 37.7 cubic feet, or 1.40 cubic yards, before waste. Add 10% for a practical order of about 1.54 cubic yards.
Do I need rebar for a round slab?
Most structural round slabs use a reinforcement grid or ring. The right bar size, spacing and cover depend on the load and soil; confirm the layout with a licensed engineer or your building plan.
What is the difference between diameter and radius?
Diameter is the full width across the circle. Radius is half the diameter, measured from the center to the edge. The calculator asks for diameter and converts it to radius internally.
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